OP0112 EXPANSION OF ACTIVATED CD7+ CYTOTOXIC T CELLS AND NK CELLS IN SSC AND PREVENTION OF FIBROBLAST CONTRACTION THROUGH SELECTIVE IMMUNOTOXIN-MEDIATED DEPLETION OF THESE CELLS
Authors: T. I. Papadimitriou, P. Singh, A. Van Caam, M. Gorris, B. Walgreen, E. Vitters, M. Koenders, R. Smeets, M. Vonk, I. J. M. De Vries, P. Van der Kraan, M. Huijnen, H. Koenen, R. M. Thurlings
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic sclerosis is characterized by vasculopathy, fibrosis and autoimmune inflammation. Adaptive immune and NK cells express co-stimulatory molecules to regulate effector responses in inflammatory conditions. CD7 is a co-stimulatory molecule induced by IFN-γ signaling on T and NK cells that is downregulated upon residency in tissues such as skin [1]. <h3>Objectives</h3> Hypothetically, CD7 is upregulated in IFN-γ driven conditions, allowing targeted depletion of pathogenic cells. In this study, we analyzed expression, regulation and targeting of CD7 in SSc tissues and in a patient treated with anti-CD7 immunotoxin (CD7-IT). <h3>Methods</h3> To identify disease-specific activation markers we compared status of T cell activation in SSc skin compared to blood. To do so, single-cell RNA sequencing datasets containing 60,000 skin and blood immune cells from 109 SSc patients versus 65 healthy donors were analyzed. Twentyone-color flow cytometry (n=50) and 8-color multiplex skin immunofluorescence staining (mIF) (n=30) were used for validation and spatial localization. CD7-IT was used to induce subset-specific depletion in vitro, and ex vivo skin explants. Fibroblasts and immune cells were co-cultured in 3D collagen hydrogel to test effect of targeted immune cell depletion on fibroblast contractility. A single patient was treated with immunotoxin on compassionate use basis. <h3>Results</h3> Sc-RNAseq analysis showed that SSc skin is characterized by increased infiltration of CD7+ cells corresponding to CD8<sup>+</sup>GZMB<sup>+</sup> and CD56<sup>+</sup>GZMB<sup>+</sup> cytotoxic T and NK cells. Immunohistochemistry also showed that SSc lesional skin exhibits significantly higher infiltration of these CD7<sup>+</sup> (T and NK) cells than non-affected skin (Figure 1). Expansion of CD7<sup>+</sup> cytotoxic T cells was also observed in SSc blood. A CD7-targeting IT effectively depleted 85% of CD7<sup>+</sup> cytotoxic T and NK cells in vitro, and in ex vivo skin. Strikingly, depletion of CD7<sup>+</sup> cells prevented fibroblast activation and contraction in a 3D fibroblast-immune cells co-culture assay. Notably, also in vivo administration of CD7-IT significantly eliminated CD7<sup>+</sup> cell subsets in patient's blood and skin. <h3>Conclusion</h3> Together, we show strong presence of CD7 on SSc immune cells and that targetting this molecule depletes T and NK cell populations with potential disease modifying results. Our results pave the way for a novel approach in halting SSc related fibrosis. <h3>Reference</h3> [1]Wang T, Huang C, Lopez-Coral A, et al. K12/SECTM1, an interferon-γ regulated molecule, synergizes with CD28 to costimulate human T cell proliferation. <i>J Leukoc Biol</i>. 2012;91(3):449-459. doi:10.1189/jlb.1011498 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.